The invention relates to data imprinting devices for cameras which imprint data, such as a date, on photosensitive film. More specifically, the invention relates to a data imprinting device which imprints by exposing a dot-matrix of points on a photographic film using an array of light emitting elements activated synchronously with the feeding of the film.
Referring to FIG. 8, a data imprinting device 80, according to the prior art, employs seven light emitting diodes (LEDs) 1.about.7 arranged perpendicularly to a direction of feed of a film. A constant voltage circuit 73 feeds power from a battery 71 to a motor drive circuit 37. Constant voltage circuit 73 provides a constant voltage output despite fluctuations in the voltage of battery 71. Constant voltage circuit 73 supplies stabilized power to a CPU 17, a light emitting diode (LED) drive circuit 19 and a photo interrupter 53.
A partial pushdown switch SW1 and a full pushdown switch SW2 are connected to CPU 17. Partial pushdown switch SW1 is actuated by partial depression of a camera release button. Full pushdown switch SW2 is actuated by full depression of the camera release button. Output signals from photo interrupter 53 are input to CPU 17. Outputs from CPU 17 are connected to LED drive circuit 19 and motor drive circuit 37. A feed motor 38, for feeding film, is driven by motor drive circuit 37.
Seven LEDs 1.about.7 are connected to LED drive circuit 19. Seven output terminals A1.about.A7 of CPU 17 provide control signals on signal L1.about.L7 to corresponding input terminals B1.about.B7 of LED drive circuit 19.
The control signals on signal lines L1.about.L7 control counterpart LEDs 1.about.7, respectively. Thus, control signals from signal line L1, for example, control signals input on signal line L2 cause LED 2 to emit light, and so forth.
Referring now to FIGS. 1, 8 and 9, numerals are formed by the data imprinting synchronized with the feeding of film. Numerals are formed by activating a combination of LED1.about.LED 7 (FIG. 9), at successive intervals of time for each numeral. The time intervals are keyed to the movement of the film as the film is fed. Dot matrix patterns are thereby generated, each time interval mapping into a corresponding interval of the film. Data imprinting exposure takes place in five successive time intervals A, B, C, D and E.
The blackened circles represent exposed regions on the film for formation of the numeric character "9". The white circles represent regions on the film which remain unexposed in forming the character "9" during feeding of the corresponding interval of film.
In the conventional data imprinting device, each LED is connected to its own signal line. Thus, to control operation of, seven LEDs 1.about.7, for example, seven signal lines L1.about.L7 are required.
In addition, note that each column A through E represents an interval of film that was fed past and exposed by LEDs 1.about.7 at the same time. Therefore, up to 7 LEDs may be activated at a single time in order for the character shown in FIG. 9 to be imprinted. Thus, the conventional imprinting device must power all seven LEDs simultaneously. For example, when imprinting the points in column C for the numeral "1," seven LEDs are simultaneously lighted. If 20 mA of current is required to light each LED, the conventional device requires a constant-voltage circuit having a capacity as large as 140 mA.
In view of the recent trend toward reducing the size of cameras, the space required by components, such as signal lines and circuit elements, is a significant design issue. Thus, the ability to reduce the size, number and cost of components has positive implications for camera design.
A data imprinting device requiring fewer control signal lines would not only reduce the number of components by the number of signal lines, but also the size of the CPU. This is because the CPU requires fewer control signal outputs to drive a given number of LEDs. Thus, a camera employing a CPU with seven control signal outputs is inevitably larger and more costly than one employing a CPU with fewer control signal outputs.
The ability to reduce the peak power requirements of the LED array over that of a conventional device can also result in space and cost savings.
Another embodiment of a data imprinting device, disclosed in Japanese Laid-open Patent Publication No. 4-81831, achieves a lower peak power requirement by activating the LEDs sequentially, so that fewer LEDs are activated at a given time. But, in this device, the characters imprinted are slanted and difficult to read. In addition, successive LEDs in this device are activated before previous ones are deactivated. The device, therefore fails to take full advantage of the possible peak power reductions.